Certain orthopedic procedures are known where sections of bone are fixed together, or where prosthetic devices are fixed to bone. In recent years bone staplers have been introduced which are capable of driving hardened (e.g. titanium) staples into bone to accomplish these ends.
U.S. Pat. Nos. 4,500,025 and 4,527,726 describe devices suitable for stapling bone during an orthopedic surgical procedure. The disclosures of those two patents are hereby incorporated by reference in their entirety. Those patents describe a bone stapler with a removable staple cartridge which precludes leaving a staple in the stapler that could be inadvertently driven after the cartridge is removed. Such a cartridge includes a case that comprises guide walls defining an inner surface at the end of a stack of staples opposite a follower, and side walls projecting normal to the inner surface. Opposed openings in the inner surface align with a passageway for a staple driver when the cartridge is inserted into the stapler. Because all of the staples remain within the cartridge until they are driven, the user can be assured that all the staples are removed from the stapler when the cartridge is removed.
U.S. Pat. No. 4,569,469 and Reissue U.S. Pat. No. 33,362 (each of which are also incorporated by reference) describe a bone stapler cartridge that is less expensive to manufacture and significantly easier to use than the devices described in U.S. Pat. Nos. 4,500,025 and 4,527,726. While this device operates suitably, improvements may be made to enhance the design of the bone stapler cartridge. A review of the factors affecting the design and construction of a bone stapler cartridge highlight the advantages of the present invention.
A bone stapler according to the prior art includes a staple driver that is powered pneumatically. The staple driver provides a relatively large force that expels the staples from the staple cartridge and into bone tissue. This requires careful alignment of the staples within the staple cartridge, and the staple cartridge within the staple driving device. Any binding, skewing or misalignment of the staples within the cartridge may result in undesirable results such as malformed staples, binding of the bone stapler or destruction of the staple cartridge housing.
The variety of orthopedic surgical procedures which call for a bone staple result in a need for a variety of bone staple sizes. Typically, the same staple driving device will be used to drive a variety of different sized staples. Further, it is desirable to reduce to a minimum the number of different cartridge case sizes for which molds are required and parts have to be inventoried. For example, it is desirable that the same width of cartridge be used with all the staples of a particular width but with different leg lengths. This has been difficult to achieve in practice, however; as staples with short leg lengths have a potential to jam within a cartridge designed to accommodate the same width staples with longer leg lengths.
One known solution to this dilemma is embodied in staple cartridges sold by 3M Company of St. Paul, Minn. as e.g. Cat. No. 7615 bone stapler cartridges. These cartridges are constructed with a spacer block within an outer case, both pieces formed as individual polymeric moldings which are then fused or solvent welded to each other. The spacer block then can help guide the pointed legs of the generally U-shaped staples toward the staple outlet of the driver.
Several problems are associated with the fusing or solvent welding step during assembly. First, a solvent has the potential to mar, deform, streak, misalign and/or weaken the polymeric housing elements thereby increasing the incidents of defective housings encountered during assembly and construction, and increasing the risk that the staples will be exposed to the adhesive. Second, the adhesive requires a dwell time that increases the time required to construct a bone staple cartridge. Third, capillary action can carry the typically thin solvent to areas where it is unwanted.
While defective cartridges do not reach the consumer, the great care and attention to detail taken during inspection procedures are time intensive. As a result, prior art procedures for assembly of a bone stapler cartridge have the capacity for improvement.
Followers according to present designs also leave room for improvement in providing even, reliable support for the stack of staples within the cartridge to avoid undesirable consequences such as jamming. The follower should a) be quickly and easily assembled without the use of adhesives or solvents, b) move the stack of staples into position robustly, and c) support each staple reliably during ejection.